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PostgreSQL uses a cost-based optimizer (CBO) to determine the best execution plan for a given query. The optimizer considers multiple alternative plans during the planning phase. Using the EXPLAIN command, a user can only inspect the chosen plan, but not the alternatives that were considered. To address this gap, I developed pg_plan_alternatives, a tool that uses eBPF to instrument the PostgreSQL optimizer and trace all alternative plans and their costs that were considered during the planning phase.

As a PostgreSQL expert, one of the most common “ghosts” I hunt during database audits is the zombie session. You know the one: a backend process that stays active or idle in transaction, holding onto critical locks and preventing vacuum from doing its job, all because the client disappeared without saying goodbye. In the words of Miracle Max from The Princess Bride, there’s a big difference between mostly dead and all dead.

Part 2 of the Semantic Caching in PostgreSQL series that’ll take you from a working demo to a production-ready system.

© Laurenz Albe 2026

PostgreSQL has supported the (non-standard) ON CONFLICT clause for the INSERT statement since version 9.5. In v19, commit 88327092ff added ON CONFLICT ... DO SELECT. A good opportunity to review the benefits of ON CONFLICT and to see how the new variant DO SELECT can be useful!